1. Technical Field
This invention generally relates to driven, trailerable, cement mixer having an integral polyethylene cement mixing drum.
2. Background Art
It has been well known for a number of years that cement does not readily adhere to most polymer surfaces, and in particular to polyethylene materials. It has been well known for a much longer period of time that cement will readily adhere to steel and other metallic surfaces, particularly if the coefficients of expansion and contraction are similar. Yet given this knowledge, cement mixers of any reasonable capacity have always utilized steel mixing drums as opposed to polyethylene which is one of the strongest polymer materials. Only the smallest capacity cement mixers have been able to take advantage of the desirable characteristics inherent to a polyethylene mixing drum, primarily because of the forces that need be imparted to a polyethylene drum in order to rotate it, when it contains anything more than a few cubic feet of cement, exceed the strength limitations of a polyethylene drum resulting in either deformation of the drum, or a parting of the drum from its mechanical turning mechanism. As a result, the use of polyethylene drums for cement mixers is generally restricted to hand operated, small capacity, cement mixing devices. Examples can be found in Bishop U.S. Pat. Nos. 4,491,415, 4,634,284 and 4,750,840.
As the capacity of the cement mixer is increased, the need for structural strength for the drum increases and as a result, in order to take advantage of the non-stick Properties of polyethylene, manufactures of cement mixers have resorted to the use of polyethylene liners held within a steel drum. An example of this design can be seen in Adsit, U.S. Pat. No. 4,521,116.
Cement mixers having steel drums without a liner must be carefully and promptly cleaned after each use to prevent the buildup of dried cement within the drum. This is a time consuming and often neglected task. Failure to clean the drum promptly and completely results is a drastically shortened life for the drum. As a result, replacement drums must be periodically installed in trailerable, powered cement mixers in the four to twelve cubic feet capacity range.
Even the use of the polyethylene liner is, in and of itself, not an entirely satisfactory solution since it must still be promptly cleaned before the cement residue dries. The reason for this is that, once the residue dries on the polyethylene surface, it has to be either scrapped off or jarred loose. The easiest way to remove the dried cement residue is to jar it loose by striking a blow to the drum, which usually results in the dried cement separating from the surface of the polyethylene drum and coming to rest as a pile of cement powder at the bottom of the drum. This powder can then be quickly and easily dumped from the drum. Even in situations where the interior surfaces of the polyethylene drum liner are promptly cleaned, the residue will collect and adhere to the bottom surface of the drum liner. However, if the polyethylene liner is encased within a metal outer shell, a blow to the outer shell with a hammer or other heavy object to jar the dried cement residue loose will dent and permanently deform the metal drum shell, which defeats the purpose of using the polyethylene liner in the first place. Thus, if the dried cement residue is located at the bottom of the drum, it is almost invariably in a location where the drum liner is totally encased within the metal shell. As a result the cement mixers in the four to twelve cubic foot capacity range being manufactured today are still formed with conventional steel cement mixing drums.
Accordingly, it is an object of this invention to provide a powered, trailerable, cement mixer with a capacity of between four and ten cubic feet which utilizes a polyethylene cement mixing drum having all of its surfaces, including the base of the drum, exposed or otherwise not encased within a steel or other metal type shell.
A second object of the present invention is to provide for polyethylene mixing blades and shovels as opposed to blades and shovels formed of metal, attached within the mixing drum.